The long-terms of this project is to learn how the Ser genes are regulated in Tetrahymena thermophila and how the various regulatory levels are integrated. This requires cloning of additional Ser genes and the further molecular characterization of mutants defective in the expression of Ser genes. This project has three specific aims: 1) to clone Ser genes and determine their regulation; 2) to characterize Ser expression in mutants and natural isolates with altered patterns of Ser expression; 3) to isolate and characterize additional regulatory Ser mutants, including suppressors of one implicated in mRNA stability. The results will allow formulation of predictive models and testable hypotheses for future research. The results will be relevant to the similar interlocked expression of surface protein genes in medically important parasitic protist and to the general problem of eukaryotic gene regulation in signaling and development.